Motorcycle Reed Valve Systems

In a two-stroke engine, the piston works like a pump sucking the fresh air-fuel mixture into the crankcase. Does the motor really need a check valve in the air intake? Of course, it can work perfectly well using just a plain piston-port system, but the valve allows for increasing engine performance. There are two main kinds of such devices – the rotary disc valves, which were popular in the 60s, and the reed ones. The former are much more complex, more expensive, and less reliable. The latter are simpler and good enough for most applications including motocross.

Installed between the engine and carburetor, or even bolted directly to the crankcase, the reed valve prevents some part of the mixture from going back to the intake thus ensuring more power. Typically, it's composed of two or more flexible petals mounted onto a wedge-shaped cage. When the piston creates a low-pressure zone in the crankcase, these petals open to let the mixture inside the engine. The number, material, and size of these parts can differ in various models, but the main principle remains the same. However, there are some traits peculiar to each model, and they influence the valve's lifespan and its efficiency at low or high RPM.

The cage's design can also vary influencing performance. In general, its volume has to be approximately the same as the volume of the crankcase and carburetor in order not to create restrictions to the flow. There can be multiple shorter petals or one large petal laying over another one, like in a dual-stage system by Boyesen; such solutions are meant for better throttle response and higher torque throughout the powerband. Our online store offers reed valves, rebuild kits, gaskets, boots, and related components made by Moto Tassinari, Boyesen, and other reliable companies that dominate the market these days. We carry both carbon fiber and fiberglass reeds featuring sufficiently light weight and durability to meet the highest expectations.